Adsorption of Bacteriophages to Homologous Bacteria 



Measurement of the Adsorption Velocity. 



In order to test equation (1), we shall determine, as a function of time, the in- 

 fectivity of mixtures of known concentration of heat-killed bacteria and input 

 bacteriophages, so that the value of the expression 



2 3 no 

 k = -r- los; — • 

 bt ^ nt 



whose constancy is demanded by equation (1), can be calculated. 



These experiments are carried out in the following way. A heat-killed bac- 

 terial suspension of known concentration is diluted into broth, so that after ad- 

 dition of the phage the concentration of bacteria in the reaction mixture is 6. 

 After this dilution has been warmed to 37°, a measured amount of a lysate di- 

 lution of exactly known phage titer is added and the time noted. In order to keep 

 the temperature constant, the reaction mixture is placed in an incubator, in the 

 case of long experiments, or, otherwise, in a water bath. After various times have 

 elapsed, a measured aliquot of the reaction mixture is quickly diluted 10 or 100- 

 fold, so that for all practical purposes, the reaction is stopped ^ In this manner, 

 reaction times down to 2 minutes can be investigated, after some practice. For 

 reaction times of more than 1 hour, in cases where the anticipated titer permits 

 this procedure, the sample is plated directly on agar plates. Under the present 

 experimental conditions it is unnecessary to separate the dead bacteria from the 

 reaction mixture before plating, since only irreversible adsorption is involved. 



The detailed results of one experiment, and the calculations based thereon, 

 shall be presented here as an illustration. 0.25 ml of the heat-killed broth culture 

 of coli bacteria, containing 4 X 10* bacteria ml, was added to 4.65 ml broth. 

 After warming the bacterial suspension to 37°, 0.1 ml of a thousand-fold dilution 

 of a lysate of titer 8.5 X 10* was added to it. The mixture was placed in the incu- 

 bator; after 1, 2, and 3 hours, 0.1 ml aliquots were removed from the mixture and 

 spread at once on agar plates. The initial titer of the mixture, n<„ was 1.7 X 10*; 

 the titers, after 1, 2, and 3 hours were found to be 5.8 X 10^ 2.4 X 10^ and 7.2 

 X 10^ With the known value of 6 = 2.0 X 10^ and the time measured in 

 seconds, k can be calculated. 



After 1 hour 



2^3 Tio ^ 2.3 1.7 X 10^ 



ht ^^ nt 2 X 10^ X 3600 ^^ 5.8 X 10 » 



After 2 hours 

 After 3 hours 



= 3.2 X 10- 11 log 2.9 = 1.5 X 10-" 



3 2 X 10- " 

 J. _ '^- -r ^^ log 7.1 = 1.4 X 10-" 



3 9 V 10"" 

 k = •^- ^^^ log 23.6 = 1.5 X 10-" 



^A 100-fold dilution reduces the reaction velocity by a factor of 100. 



27 



